Radio communication apparatus and method of handover from a macro cell to a closed subscribers group cell

ABSTRACT

When a handover request for performing a handover of a terminal ( 70 ) from a macro cell C1 to a CSG cell C2 is received from an SeNB  10  (S 8 ), a base station (TeNB) ( 40 ) of the CSG cell C2 transmits a handover response in accordance with a handover enabled/disabled state (S 12 ). The handover response includes an identifier of the terminal ( 70 ) in the CSG cell C2. Upon receiving the response, the SeNB ( 10 ) notifies the identifier to the terminal ( 70 ) (S 14 ). The TeNB ( 40 ) repeatedly transmits a dedicated signal containing a handover command via a dedicated channel set using the identifier at an interval shorter than a gap period (S 18 ). Accordingly, whether or not access is permitted can be judged promptly and a smooth handover can be realized.

CROSS-REFERENCE(S) TO RELATED APPLICATION(S)

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2008-023207, filed on Feb. 1, 2008, andfrom Japanese Patent Application No. 2008-118558, filed on Apr. 30,2008, the disclosures of which are incorporated herein in its entiretyby reference.

BACKGROUND Technical Field

The present invention relates to a handover technique, and particularly,to a technique for performing a handover by judging whether or notaccess by a terminal to a cell that is a handover destination ispermitted or not.

Description of the Related Art

Techniques for performing a handover of a terminal engaged incommunication between different cells have been conventionally known.For example, Section 10.1.2.1.1 of “3GPP TS 36.300 V8.3.0” prescribes aprocedure of a handover between macro cells. FIG. 21 is a flow chart ofa handover described in “3GPP TS 36.300 V8.3.0”. Hereinafter, aconventional handover procedure will be described with reference to FIG.21.

First, a terminal (UE: User Equipment) receives a signal from aneighboring base station and measures propagation path quality. Theterminal notifies a measurement result to a currently-connected basestation (Source eNB, hereinafter referred to as “SeNB”) by means of ameasurement report (“2. MEASUREMENT REPORTS” illustrated in FIG. 21).The measurement report includes a cell identifier (cell ID) of a basestation having good propagation path quality as seen from the terminal,access information of the terminal (Tracking Area ID, hereinafterreferred to as “TAID”), and the like. The SeNB determines a base stationwith a good propagation path status as a handover destination basestation (Target eNB, hereinafter referred to as “TeNB”) of the terminal.

The SeNB has a list of neighbor cells (Neighbor Cell List, hereinafterreferred to as “NCL”). An NCL is a list of cell IDs of base stationsneighboring the SeNB, access information (TAID), and the like. The SeNBuses the NCL to transmit a handover request signal (“4. HANDOVERREQUEST” illustrated in FIG. 21) to a base station (TeNB) correspondingto a cell ID notified by the measurement report.

Upon receiving the handover request signal, the TeNB determines whetheror not a handover can be performed based on the status of remainingresources and the like. When the TeNB determines that a handover can beperformed, the TeNB transmits a handover response signal (“6. HANDOVERREQUEST ACKNOWLEDGE” illustrated in FIG. 21) to the SeNB.

Upon receiving the handover response signal, the SeNB transmits ahandover execution instruction signal (“7. HANDOVER COMMAND” illustratedin FIG. 21) to the terminal. The handover execution instruction includesinformation necessary for the terminal for subsequent uplinksynchronization such as a terminal identification ID (C-RNTI) in theTeNB.

Upon receiving the handover execution instruction, the terminaltransmits a Random Access Preamble to the handover destination basestation (TeNB) and starts the uplink synchronization (“9.SYNCHRONIZATION” illustrated in FIG. 21). Upon receiving the RandomAccess Preamble, the TeNB performs an uplink allocation for the terminaland notifies allocation information to the terminal (“10. ULALLOCATION+TA FOR UE” illustrated in FIG. 21). When connection with theTeNB is successful, the terminal transmits a handover confirmationsignal (“11. HANDOVER CONFIRM” illustrated in FIG. 21) to the TeNB andnotifies that handover processing by the terminal has been completed.This concludes a basic outline of handover processing between macrocells.

The 3GPP LTE project is evaluating installing an indoor base station(Home eNB) in a home to construct a CSG (Closed Subscriber Group) cell.A plurality of CSG cells are provided in a single macro cell. Unlike abase station of a macro cell, a base station of a CSG cell is subjectedto access restriction as seen in a table in Section 6.3.1a.3 in “3GPP TS36.331 V8.0.0”. Therefore, a terminal is only able to connect to anaccess-permitted base station. Even if the terminal detects a basestation with exceptional propagation path quality, the terminal isunable to connect to the base station without access permission.

BRIEF SUMMARY Problems to be Solved by the Invention

In order to confirm whether or not access to a base station of a CSGcell is permitted, the terminal must confirm a TAID contained in aScheduling Unit (hereinafter referred to as “SU-1”) that is a systeminformation transmitted from the base station. The terminal collates itsown TAID and the TAID of the base station, and if the two TAIDs match,determines that access to the base station is permitted.

A signal transmitted from the base station of a CSG cell may sometimesbe communicated over a different frequency from a signal transmittedfrom the base station of a macro cell. In this case, in order to receivean SU-1 transmitted from the base station and confirm whether or notaccess is permitted, the terminal must temporarily suspend communicationwith the base station of the macro cell. In the present specification, aperiod during which communication with the base station of the macrocell is temporarily suspended shall be referred to as a “gap period”.Even during a gap period, the terminal is capable of detecting a radiowave from a cell being communicated over a different frequency band.

Since a CSG cell has the characteristics described above, the terminalmust conceivably receive an SU-1 transmitted from the handoverdestination during the gap period and determine whether or not access tothe CSG cell that is the handover destination is permitted.

FIG. 22 is a diagram illustrating, based on specifications currentlybeing formulated, operations during a handover from a base station of amacro cell to a base station of a CSG cell. Note that the flow depictedin FIG. 22 is a virtual flow that attempts to describe improvements inthe flow currently being formulated in an easily comprehensible manner,and is not heretofore known. In FIG. 22, UE denotes a terminal, SeNBdenotes a base station of a macro cell that is a handover source, andTeNB denotes a base station of a CSG cell that is a handoverdestination. The TeNB periodically transmits an SU-1 to the terminal.Due to time sharing that switches between a period where a signaltransmitted from the SeNB is received and a period where a signaltransmitted from the TeNB is received (gap period), the terminalreceives signals from both base stations having different frequencies.

The terminal detects radio waves of the SeNB and the TeNB, and transmitsa report on the reception qualities of the radio waves to the SeNB thatis in communication with the terminal. The SeNB judges whether ahandover should be performed or not based on the reception qualities ofthe SeNB and the TeNB. For example, the SeNB compares the receptionqualities of the SeNB and the TeNB and judges that a handover to theTeNB should be performed when the reception quality of the TeNB isbetter than the reception quality of the SeNB. When a handover should beperformed, a handover request is transmitted to the TeNB. Havingreceived the handover request, the TeNB judges a handoverenabled/disabled state based on whether there are resources forconnecting a new terminal and the like, and transmits a handoverresponse to the SeNB. In this case, let us assume that the TeNB sends ahandover OK response.

Next, based on the report from the terminal, the SeNB determines whetheraccess from the terminal to the TeNB is permitted or not. Morespecifically, upon receiving the SU-1, the terminal detects a TAID inthe SU-1, compares the terminal TAID with the SeNB TAID, and judgeswhether access is possible or not. The terminal includes accesspermission information in the measurement report and transmits the sameto the SeNB. When access from the terminal to the base station ispermitted, the SeNB transmits a handover command to the terminal. Uponreceiving the handover command, the terminal transmits a RACH preambleto the SeNB and performs an operation to connect to the TeNB. Thefollowing operations have been omitted from FIG. 22.

As illustrated in FIG. 22, in order to judge whether or not access to anSeNB that is the handover destination is permitted, the terminal mustreceive an SU-1 transmitted from the SeNB. Unless an SU-1 is transmittedduring a gap period, there will be no more opportunities to receive anSU-1 until the next gap period. In addition, there is no guarantee thatan SU-1 will be transmitted at a timing that coincides with the next gapperiod. For example, according to the specifications currently beingformulated, a gap period exists every several 10 ms and only has alength of 6 ms. Unless an SU-1 is transmitted during a 6-ms gap period,there will be no more opportunities to receive an SU-1 until the nextgap period. In addition, there is no guarantee that an SU-1 will betransmitted at a timing that coincides with the next gap period.Therefore, a judgment of whether or not access is permitted may taketime and may result in a time-consuming handover operation.

Accordingly, in consideration of the background described above, it isan object of the present invention to provide a base station and a radiocommunication system capable of promptly judging whether access ispermitted or not and realizing a handover in a smooth manner.

Means for Solving the Problems

A radio communication system according to the present inventioncomprises a first base station that controls communication with aterminal in a first cell and a second base station that controlscommunication with a terminal in a second cell contained in the firstcell, wherein: the first base station transmits a handover request forperforming a handover of the terminal from the first cell to the secondcell to the second base station; the second base station transmits ahandover response that is a response to the handover request and whichincludes an identifier of the terminal in the second cell to the basestation of the first cell; the first base station notifies theidentifier contained in the handover response to the terminal; and thesecond base station repeatedly transmits a dedicated signal containing ahandover command via a dedicated channel set using the identifier at aninterval shorter than a period during which the terminal is able toreceive data from the base station of the second cell.

A radio communication system according to another aspect of the presentinvention comprises a first base station that controls communicationwith a terminal in a first cell and a second base station that controlscommunication with a terminal in a second cell contained in the firstcell, wherein: the first base station transmits a handover request forperforming a handover of the terminal from the first cell to the secondcell to the second base station; the second base station transmits ahandover response that is a response to the handover request to the basestation of the first cell; and the second base station shortens atransmission interval of a system information containing accessinformation to be transmitted through a common channel in comparison tobefore receiving the handover request when performing a handover inresponse to the handover request.

As will be described below, the present invention also includes otheraspects. As such, the disclosure of the present invention is intended toprovide a part of the present invention and is not intended to limit thescope of the present invention as described and claimed herein.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram illustrating operations during a handover by a radiocommunication system according to a first embodiment;

FIG. 2 is a diagram illustrating an overall configuration of a radiocommunication system according to the first embodiment;

FIG. 3 is a diagram illustrating a configuration of an SeNB according tothe first embodiment;

FIG. 4 is a diagram illustrating a configuration of a TeNB according tothe first embodiment;

FIG. 5 is a diagram illustrating an example of a flow of signalstransmitted and received during a handover according to the firstembodiment;

FIG. 6 is a diagram illustrating a configuration of an SeNB according toa second embodiment;

FIG. 7 is a diagram illustrating a configuration of a TeNB according tothe second embodiment;

FIG. 8 is a diagram illustrating operations during a handover accordingto the second embodiment;

FIG. 9 is a diagram illustrating an example of a flow of signalstransmitted and received during a handover according to the secondembodiment;

FIG. 10 is a diagram illustrating an example of a flow of signalstransmitted and received during a handover according to the secondembodiment;

FIG. 11 is a diagram illustrating operations during a handover accordingto another aspect of the second embodiment;

FIG. 12 is a diagram illustrating an example of a flow of signalstransmitted and received during a handover according to another aspectof the second embodiment;

FIG. 13 is a diagram illustrating an example of a flow of signalstransmitted and received during a handover according to another aspectof the second embodiment;

FIG. 14 is a diagram illustrating operations during a handover accordingto a third embodiment;

FIG. 15 is a diagram illustrating an example of a flow of signalstransmitted and received during a handover according to the thirdembodiment;

FIG. 16 is a diagram illustrating operations during a handover accordingto another aspect of the third embodiment;

FIG. 17 is a diagram illustrating an example of a flow of signalstransmitted and received during a handover according to another aspectof the third embodiment;

FIG. 18 is a diagram illustrating operations during a handover accordingto a fourth embodiment;

FIG. 19 is a diagram illustrating an example of a flow of signalstransmitted and received during a handover according to the fourthembodiment;

FIG. 20 is a diagram illustrating an example of a flow of signalstransmitted and received during a handover according to the fourthembodiment;

FIG. 21 is a flow chart of a handover described in “3GPP TS 36.300V8.3.0”;

FIG. 22 is a virtual diagram illustrating operations during a handoverfrom a base station of a macro cell to a base station of a CSG cell;

FIG. 23 is a diagram illustrating a configuration of an SeNB accordingto a fifth embodiment;

FIG. 24 is a diagram illustrating a configuration of a terminalaccording to the fifth embodiment;

FIG. 25 is a diagram illustrating operations during a handover accordingto the fifth embodiment;

FIG. 26 is a diagram illustrating an example of a flow of signalstransmitted and received during a handover according to the fifthembodiment;

FIG. 27 is a diagram illustrating an example of a flow of signalstransmitted and received during a handover according to the fifthembodiment;

FIG. 28 is a diagram illustrating a configuration of an eNB of a system2 according to a sixth embodiment;

FIG. 29A is a diagram illustrating an example of an access-prohibitedcell list;

FIG. 29B is a diagram illustrating a CSG cell list;

FIG. 30 is a diagram illustrating an example of a new access-prohibitedcell list;

FIG. 31 is a diagram illustrating another example of a newaccess-prohibited cell list;

FIG. 32 is a diagram illustrating a configuration of a UE of the system2 according to the sixth embodiment; and

FIG. 33 is a diagram illustrating an operation for extracting anaccess-prohibited cell list performed by a UE of the system 2 accordingto the sixth embodiment.

DETAILED DESCRIPTION

Hereinafter, a detailed description of the present invention will begiven. It is to be understood that the embodiments of the presentinvention described hereinafter are illustrative only and variousmodifications can be made thereon. As such, the specific configurationsand functions disclosed below are not intended to limit the scope of thepresent invention.

A base station according to an embodiment controls, in a networkincluding a first cell and a second cell contained in the first cell,communication with a terminal in the second cell, the base stationcomprising: a handover request receiver that receives a handover requestfor performing a handover of the terminal from the first cell to thesecond cell from a base station of the first cell; a handover responsetransmitter that transmits a handover response that is a response to thehandover request and which includes an identifier of the terminal in thesecond cell to the base station of the first cell, and causes the basestation of the first cell to notify the identifier to the terminal; anda dedicated signal transmitter that repeatedly transmits a dedicatedsignal containing a handover command to the terminal via a dedicatedchannel set using the identifier at an interval shorter than a periodduring which the terminal is able to receive data from the base stationof the second cell.

As described above, the base station of the second cell transmits ahandover response including an identifier in response to a handoverrequest to the base station of the first cell, and causes the basestation of the first cell to notify the identifier to the terminal.Accordingly, a dedicated signal can be transmitted to the terminal usinga dedicated channel by merely performing a process of returning ahandover response to the base station of the first cell. In addition,since a transmission interval of the dedicated signal is set shorterthan a period during which the terminal is able to receive data from thebase station of the second cell, the terminal is able to receive thededicated signal during a first receivable period after the start oftransmission of the dedicated signal and a handover can be performed ina short period of time.

The base station may further comprise a RACH preamble command receiverthat receives a RACH preamble command transmitted from the terminal inaccordance with the dedicated signal, wherein the dedicated signaltransmitter may stop transmission of the dedicated signal when the RACHpreamble command is received or when a predetermined period of time haslapsed from the start of transmission of the dedicated signal.

By stopping transmission of the dedicated signal when a predeterminedperiod of time has lapsed as described above, in the event that ahandover of the terminal to the second cell is not performed, the basestation of the second cell can release resources of the dedicatedchannel at an appropriate timing.

A base station according to another embodiment controls, in a networkincluding a first cell and a second cell contained in the first cell,communication with a terminal in the second cell, the base stationcomprising: a handover request receiver that receives a handover requestfor performing a handover of the terminal from the first cell to thesecond cell from a base station of the first cell; a handover responsetransmitter that transmits a response to the handover request to thebase station of the first cell; and a system information transmitterthat transmits a system information containing access informationthrough a common channel, wherein the system information transmittershortens a transmission interval of the system information as comparedto before receiving the handover request when performing a handover inaccordance with the handover request.

As described above, the base station of the second cell shortens atransmission interval of a system information as compared to beforereceiving a handover request when performing a handover in accordancewith the handover request. Accordingly, the probability of the terminalfailing to receive the system information can be lowered and a handovercan be performed in a short period of time. Moreover, by setting thetransmission interval of the system information shorter than a periodduring which data is receivable from the base station of the secondcell, the system information can be received during a first receivableperiod.

The base station may further comprise a RACH preamble command receiverthat receives a RACH preamble command transmitted from the terminal inaccordance with the dedicated signal, wherein the system informationtransmitter may restore the transmission interval of the systeminformation to an original transmission interval when the RACH preamblecommand is received or when a predetermined period of time has lapsedafter shortening the transmission interval of the system information.

By stopping transmission of the dedicated signal when a predeterminedperiod of time has lapsed as described above, the base station of thesecond cell can restore resources of the common channel to an originalusage state.

A base station according to another embodiment controls, in a networkincluding a first cell and a second cell contained in the first cell,communication with a terminal in the first cell, the base stationcomprising: a measurement report receiver that receives, from theterminal, a measurement report including a cell identifier of the secondcell whose radio wave has been detected by the terminal and qualityinformation of the radio wave; a handover request transmitter thattransmits a handover request to a base station to which access from theterminal is permitted among base stations of the second cell having acell identifier judged to be a handover destination when it is judged,based on the measurement report, that a handover of the terminal fromthe first cell to the second cell should be performed; a handoverresponse receiver that receives a handover response that is a responseto the handover request and which includes an identifier of the terminalin the second cell from the second cell; and an identifier transmitterthat notifies the identifier contained in the handover response to theterminal.

By notifying the identifier included in a response to a handover requestto the terminal, a dedicated signal can be transmitted using a dedicatedchannel from the base station of the second cell to the terminal.

A base station according to another embodiment controls, in a networkincluding a first cell and a second cell contained in the first cell,communication with a terminal in the first cell, the base stationcomprising: a measurement report receiver that receives, from theterminal, a measurement report including a cell identifier of the secondcell whose radio wave has been detected by the terminal and qualityinformation of the radio wave; a handover request transmitter thattransmits a handover request to a base station of the second cell havinga cell identifier judged to be a handover destination when it is judged,based on the measurement report, that a handover of the terminal fromthe first cell to the second cell should be performed; a handoverresponse receiver that receives a handover response to the handoverrequest from the second cell; an access permission state notificationreceiver that receives information on an access permission state of thesecond cell from the terminal; and a handover command transmitter thattransmits a handover command to the terminal when access to the basestation of the second cell is permitted.

As described above, the base station of the first cell transmits ahandover request to all base stations having a cell identifier judged tobe a handover destination regardless of whether access from the terminalis permitted or not. Accordingly, the base station of the second cellcan transmit information regarding access permission to the terminal.For example, by having the base station of the second cell transmit asystem information containing access information at an interval that isshorter than an ordinary system information transmission interval, theterminal can promptly comprehend whether access to the base station ofthe second cell is permitted or not.

In the base station described above, the handover request transmittermay transmit the handover request to a base station to which access fromthe terminal is permitted among base stations of the second cell havinga cell identifier to which it is judged that a handover should beperformed based on the measurement report.

As described above, the base station of the first cell transmits ahandover request to a base station accessible by the terminal among basestations of the second cell having a cell identifier judged to be ahandover destination. Accordingly, since resources for transmitting ahandover request can be saved and the number of base stations of thesecond cell receiving the handover request can be reduced, theprocessing load on base stations of the second cell can be alleviated.

A base station according to another embodiment comprises: a receiverthat receives a measurement report from a terminal; a judging unit thatjudges whether a handover of the terminal should be performed or notbased on the received measurement report; and a transmitter thattransmits, when it is judged that a handover of the terminal should beperformed, an instruction for changing a transmission frequency of asystem information to a base station device that is a handoverdestination.

As described above, by shortening the transmission interval of a systeminformation to be transmitted by the base station of the handoverdestination as compared to before the judgment to perform a handover ismade, the probability of the terminal failing to receive the systeminformation can be lowered and a handover can be performed in a shortperiod of time. Moreover, by setting the transmission interval of thesystem information shorter than a period during which data is receivablefrom the base station of the second cell, the system information can bereceived during a first receivable period.

The base station according to the present invention may further comprisea handover command transmitter that transmits a handover commandincluding a reception instruction of a system information to betransmitted from a base station that is a handover destination to theterminal when a handover-permitted response is received from the basestation that is the handover destination.

Accordingly, the terminal may switch to processing for receiving asystem information to be transmitted from the base station of thehandover destination so as to reliably receive the system information.

A radio communication system according to the present inventioncomprises a first base station that controls communication with aterminal in a first cell and a second base station that controlscommunication with a terminal in a second cell contained in the firstcell, wherein: the first base station transmits a handover request forperforming a handover of the terminal from the first cell to the secondcell to the second base station; the second base station transmits ahandover response that is a response to the handover request and whichincludes an identifier of the terminal in the second cell to the basestation of the first cell; the first base station notifies theidentifier contained in the handover response to the terminal; and thesecond base station repeatedly transmits a dedicated signal containing ahandover command to the terminal via a dedicated channel set using theidentifier at an interval shorter than a period during which theterminal is able to receive data from the base station of the secondcell.

As described above, since the first base station notifies an identifierof the terminal in the second cell to the terminal, the second basestation can transmit a dedicated signal to the terminal using adedicated channel by merely performing a process of returning a handoverresponse to the base station of the first cell. In addition, since atransmission interval of a dedicated signal including a handover commandis set shorter than a period during which data can be received from thebase station of the second cell, the terminal is able to receive thededicated signal during a first receivable period after the start oftransmission of the dedicated signal and a handover can be performed ina short period of time.

A radio communication system according to another embodiment comprises afirst base station that controls communication with a terminal in afirst cell and a second base station that controls communication with aterminal in a second cell contained in the first cell, wherein: thefirst base station transmits a handover request for performing ahandover of the terminal from the first cell to the second cell to thesecond base station; the second base station transmits a handoverresponse that is a response to the handover request to the base stationof the first cell; and the second base station shortens a transmissioninterval of a system information containing access information to betransmitted through a common channel in comparison to before receivingthe handover request when performing a handover in response to thehandover request.

As described above, when the second base station receives a handoverrequest, by shortening the transmission interval of a system informationto be transmitted as compared to before receiving the handover request,the probability of the terminal failing to receive the systeminformation can be lowered and a handover can be performed in a shortperiod of time. Moreover, by setting the transmission interval of thesystem information shorter than a period during which data is receivablefrom the base station of the second cell, the system information can bereceived during a first receivable period.

A handover method according to the present invention is to be performedby a base station that controls, in a network including a first cell anda second cell contained in the first cell, communication with a terminalin the second cell, the handover method comprising the steps of:receiving a handover request for performing a handover of the terminalfrom the first cell to the second cell from a base station of the firstcell; transmitting a handover response that is a response to thehandover request and which includes an identifier of the terminal in thesecond cell to the base station of the first cell, and causing the basestation of the first cell to notify the identifier to the terminal; andrepeatedly transmitting a dedicated signal containing a handover commandto the terminal via a dedicated channel set using the identifier at aninterval shorter than a period during which the terminal is able toreceive data from the base station of the second cell.

As described above, the base station of the second cell transmits ahandover response including an identifier in response to a handoverrequest and causes the base station of the first cell to notify theidentifier to the terminal. Accordingly, the base station of the secondcell can transmit a dedicated signal to the terminal using a dedicatedchannel by merely performing a process of returning a handover responseto the base station of the first cell. In addition, since a transmissioninterval of the dedicated signal is set shorter than a period duringwhich the terminal is able to receive data from the base station of thesecond cell, the terminal is able to receive the dedicated signal duringa first receivable period after the start of transmission of thededicated signal and a handover can be performed in a short period oftime.

A handover method according to another embodiment is to be performed bya base station that controls, in a network including a first cell and asecond cell contained in the first cell, communication with a terminalin the second cell, the handover method comprising the steps of:receiving a handover request for performing a handover of the terminalfrom the first cell to the second cell from a base station of the firstcell; transmitting a response to the handover request to the basestation of the first cell; and shortening a transmission interval of asystem information containing access information to be transmittedthrough a common channel in comparison to before receiving the handoverrequest when performing a handover in response to the handover request.

As described above, by shortening the transmission interval of a systeminformation as compared to before receiving the handover request when ahandover request is received, the probability of the terminal failing toreceive the system information can be lowered and a handover can beperformed in a short period of time. Moreover, by setting thetransmission interval of the system information shorter than a periodduring which data is receivable from the base station of the secondcell, the system information can be received during a first receivableperiod.

Hereinafter, a radio communication system and a base station accordingto embodiments of the present invention will be described with referenceto the drawings.

First Embodiment

FIG. 1 is a flow chart illustrating operations of a handover performedby a radio communication system according to a first embodiment.Configurations of the radio communication system and a base station willnow be described before presenting a description of a handoveroperation.

FIG. 2 is a diagram illustrating an overall configuration of a radiocommunication system 1. The radio communication system 1 comprises abase station 10 of a macro cell C1, base stations 40 of a plurality ofCSG cells C2 contained in the macro cell C1, and a terminal 70. Since ahandover from a base station of the macro cell C1 to a base station ofthe CSG cell C2 will be described in the present embodiment, a basestation 10 of the macro cell C1 shall be denoted as “SeNB 10” and basestations 40 of the CSG cell C2 as “TeNB 40”. Note that the macro cell C1corresponds to the “first cell” and the CSG cell C2 to the “second cell”as respectively set forth in the claims.

The CSG cell C2 is given a cell ID. Although a cell ID is an identifierof the cell, there may be cases where cells having the same ID exist inthe macro cell C1. The CSG cell C2 has a TAID as access information. Thebase station of the CSG cell C2 permits access from a terminal 70 havingthe same TAID.

FIG. 3 is a diagram illustrating a configuration of the base station(SeNB) 10 that is a handover source. The SeNB 10 comprises a basestation communication interface (eNB Communication IF) 12 that is acommunication interface with the TeNB 40 of the CSG cell C2, a terminalcommunication interface (UE Communication IF) 14 that is a communicationinterface with the terminal 70, an NCL 16 storing information onneighbor cells, and a controller 18 that controls communication with theTeNB 40 and the terminal 70. The NCL 16 contains cell IDs, accessinformation (TAID), and the like of base stations neighboring the SeNB.

The controller 18 comprises a measurement report receiver 20, a handoverjudging unit 22, a handover request transmitter 24, a handover responsereceiver 26, and an identifier transmitter 28. Moreover, while FIG. 3illustrates a configuration necessary for performing a handover, theSeNB 10 has configurations necessary for communication control and thelike in addition to the configuration described above.

The measurement report receiver 20 receives a measurement reporttransmitted from the terminal 70. The measurement report contains a cellID of a base station whose radio wave is detected by the terminal 70 andinformation on the reception quality of the radio wave. The handoverjudging unit 22 judges whether or not a handover should be performedbased on the measurement report. For example, the handover judging unit22 compares the reception qualities of the SeNB 10 and the TeNB 40, andjudges that a handover to the TeNB 40 should be performed when thereception quality of the TeNB 40 is better than that of the SeNB 10.When the HO judging unit 22 judges that a handover should be performed,the handover request transmitter 24 transmits a handover request (HOrequest) to the base station of the handover destination. The handoverrequest transmitter 24 determines a cell ID and a TAID of the CSG cellC2 using data in the NCL 16. Subsequently, the handover requesttransmitter 24 transmits a handover request to CSG cells C2 having thesame TAID as the TAID of the terminal 70 that is the transmission sourceof the measurement report among the CSG cells C2 having the cell IDnotified in the measurement report from the terminal 70. The handoverresponse receiver 26 receives a handover response (HO response)transmitted from the TeNB 40 in response to the handover request. Theidentifier transmitter 28 transmits an identifier contained in thehandover response to the terminal 70.

FIG. 4 is a diagram illustrating a configuration of the base station(TeNB) 40 that is the handover destination. The TeNB 40 comprises a basestation communication interface (eNB Communication IF) 42 that is acommunication interface with the SeNB 10 of the macro cell C1, aterminal communication interface (UE Communication IF) 44 that is acommunication interface with the terminal 70, and a controller 46 thatcontrols communication with the SeNB 10 and the terminal 70.

The controller 46 comprises a handover request receiver 48, a handoverenabled/disabled state judging unit 50, a handover response transmitter52, a dedicated signal transmitter 54, and a RACH preamble receiver 56.Moreover, while FIG. 4 illustrates a configuration necessary forperforming a handover, the TeNB 40 has configurations necessary forcommunication control and the like in addition to the configurationdescribed above.

The handover request receiver 48 receives a handover request transmittedfrom the SeNB 10. The handover enabled/disabled state judging unit 50judges whether a handover is enabled or disabled based on whether thereare new resources that can be allocated to the terminal 70, and thelike. The handover response transmitter 52 transmits a handover responsein response to the handover request. In this case, the handover responsecontains an identifier to be used by the TeNB 40 to identify theterminal 70 in the second cell. When it is judged that a handover can beperformed, the dedicated signal transmitter 54 transmits a dedicatedsignal containing a handover command to the terminal 70 using adedicated channel. The RACH preamble receiver 56 receives a RACHpreamble transmitted from the terminal 70.

Next, operations of the radio communication system according to thefirst embodiment will be described with reference to FIG. 1. FIG. 1illustrates operations during a handover of the terminal 70, incommunication with the SeNB 10, to the TeNB 40. The terminal 70periodically transmits a measurement report to the SeNB 10 (S2). TheSeNB 10 compares the reception quality of a radio wave from the SeNB 10with the reception quality of a radio wave from the TeNB 40 to judgewhether or not a handover should be performed (S4). For example, whenthe reception quality of a radio wave from the TeNB 40 is better thanthe reception quality of a radio wave from the SeNB 10 by apredetermined threshold or more, the SeNB 10 judges that a handovershould be performed. When the reception quality of the radio wave fromthe SeNB 10 is better than that of the TeNB 40, the SeNB 10 judges thata handover should not be performed. When it is judged that a handovershould not be performed (NO in S4), the SeNB 10 awaits the reception ofa next measurement report.

When it is judged that a handover should be performed (YES in S4), theSeNB 10 extracts TeNBs 40 having an identifier corresponding to the cellID notified in the measurement report from the NCL 16. Subsequently, theSeNB 10 determines a TeNB 40 having the same TAID as the TAID of theterminal 70 among the extracted TeNBs 40 of the CSG cell C2 (S6), andjudges whether or not the TeNB is a base station of a CSG cell (S8).When the TeNB is a CSG cell (YES in S8), a handover request istransmitted to the determined TeNB 40 (S10). When the TeNB is not a CSGcell (NO in S8), a handover of the macro cell is performed.

The TeNB 40 having received the handover request judges whether ahandover can be performed or not (S12). When a handover can be performed(YES in S12), the TeNB 40 transmits a handover response to the SeNB 10(S14). Note that FIG. 1 depicts a case where a handover can beperformed. When a handover cannot be performed (NO in S12), the radiocommunication system 1 does not perform operations of step S14 andthereafter and terminates the flow. When a handover can be performed, anidentifier of the terminal 70 with respect to the TeNB 40 is to beincluded in the handover response. In the present embodiment, a C-RNTIis used as the identifier.

Upon receiving the handover response from the TeNB 40 (S14), the SeNB 10transmits the C-RNTI contained in the handover response to the terminal70 (S16). By receiving the C-RNTI transmitted from the SeNB 10, theterminal 70 can now receive the dedicated signal addressed to theterminal 70 to be transmitted from the TeNB 40 via a dedicated channel.

When it is judged in S12 that a handover can be performed, the TeNB 40starts transmission of the dedicated signal to the terminal 70 via thededicated channel (S18). In this case, the dedicated signal includesaccess information and information contained in a handover command suchas information necessary for uplink synchronization. The TeNB 40repeatedly transmits the dedicated signal until the terminal 70 receivesthe dedicated signal and a RACH preamble is transmitted to the TeNB 40(S20). The interval of repetitive transmission of the dedicated signalfrom the TeNB 40 to the terminal 70 is to be set shorter than a gapperiod of the terminal 70.

The terminal 70 judges whether the dedicated signal has been received ornot (S22). The terminal 70 can receive the dedicated signal if thededicated signal is transmitted during the gap period of the terminal70. Upon receiving the dedicated signal (YES in S22), the terminal 70confirms whether access to the TeNB 40 has been permitted or not. In thepresent embodiment, in step S6, since the SeNB 10 only transmits ahandover request to a TeNB 40 that can be accessed from the terminal 70,the terminal 70 has been permitted access to the TeNB 40 transmittingthe dedicated signal. Therefore, a reception of the dedicated signalsignifies that access to the TeNB 40 that is the transmission source ofthe dedicated signal has been permitted. If unable to receive thededicated signal over a certain period of time (NO in S22), a judgmentof handover failure is made and transmitted to the SeNB (S24). In thiscase, “a certain period of time” signifies a period of timecorresponding to an interval between gap periods.

Upon receiving the dedicated signal, the terminal 70 starts processingfor a handover based on the handover command contained in the dedicatedsignal. Specifically, the terminal 70 transmits a RACH preamble forstarting uplink synchronization to the TeNB 40 (S26), and startsprocessing to connect to the TeNB 40. Upon receiving the RACH preamble,the TeNB 40 stops transmission of the dedicated signal (S28).

When the terminal 70 does not receive the dedicated signal over acertain period of time, the terminal 70 is conceivably approaching a CSGcell C2 to which access is not permitted. In this case, “a certainperiod of time” signifies a period of time corresponding to an intervalbetween gap periods. When a certain period of time lapses from the startof transmission of the dedicated signal, the TeNB 40 stops transmissionof the dedicated signal. This concludes the description of the radiocommunication system 1 and the base stations 10 and 40 according to thefirst embodiment.

The TeNB 40 according to the first embodiment adopts a configurationthat transmits a handover response containing a C-RNTI and causes theSeNB 10 to notify the C-RNTI to the terminal 70. Accordingly, adedicated channel of the TeNB 40 can be allocated to the terminal 70before receiving a handover command instruction and a handover processcan be performed in a smooth manner.

Next, an advantageous effect gained by transmitting the dedicated signalat a transmission interval that is shorter than the gap period will bedescribed. FIG. 5 is a diagram illustrating an example of a flow ofsignals transmitted and received during a handover by the radiocommunication system 1 according to the first embodiment. As illustratedin FIG. 5, since the TeNB 40 according to the first embodimentrepeatedly transmits the dedicated signal at a shorter interval than thegap period, at least one transmission of the individual will occurwithin a gap period. Therefore, the terminal 70 is able to reliablyreceive the dedicated signal during the first gap period and a handovercan be performed in a short period of time.

Second Embodiment

Next, a radio communication system according to a second embodiment willbe described. In the same manner as the first embodiment, a radiocommunication system according to the second embodiment comprises a basestation (SeNB) 10 of a macro cell C1, base stations (TeNBs) 40 of aplurality of CSG cells C2 contained in the macro cell C1, and a terminal70.

FIG. 6 is a diagram illustrating a configuration of the base station(SeNB) 10 that is a handover source. The SeNB 10 comprises a basestation communication interface 12 that is a communication interfacewith the TeNB 40 of the CSG cell C2, a terminal communication interface14 that is a communication interface with the terminal 70, an NCL 16storing information on neighbor cells, and a controller 18 that controlscommunication with the TeNB 40 and the terminal 70. Moreover, while FIG.6 illustrates a configuration necessary for performing a handover, theSeNB 10 has configurations necessary for communication control and thelike in addition to the configuration described above.

The controller 18 comprises a measurement report receiver 20, a handoverjudging unit 22, a handover request transmitter 24, a handover responsereceiver 26, an access permission judging unit 32, and a handovercommand transmitter 30.

The measurement report receiver 20 receives a measurement reporttransmitted from the terminal 70. The measurement report contains a cellID of a TeNB 40 whose radio wave is detected by the terminal 70 andinformation on the reception quality of the radio wave. The handoverjudging unit 22 judges whether or not a handover should be performedbased on the measurement report.

When the handover judging unit 22 judges that a handover should beperformed, the handover request transmitter 24 transmits a handoverrequest to the TeNB 40 of the handover destination. The handover requesttransmitter 24 determines a cell ID of a CSG cell using data in the NCL16. The handover request transmitter 24 transmits the handover requestto the TeNB 40 of the CSG cell C2 having the cell ID notified in themeasurement report from the terminal 70.

The handover response receiver 26 receives a handover responsetransmitted from the TeNB 40 in response to the handover request. Basedon access information contained in the measurement report transmittedfrom the terminal 70, the access permission judging unit 32 judgeswhether or not access from the terminal 70 to the TeNB 40 that is thehandover destination is permitted. The handover command transmitter 30transmits a handover command to the terminal 70.

FIG. 7 is a diagram illustrating a configuration of the base station(TeNB) 40 that is the handover destination. The TeNB 40 comprises a basestation communication interface 42 that is a communication interfacewith the SeNB 10, a terminal communication interface 44 that is acommunication interface with the terminal 70, and a controller 46 thatcontrols communication with the SeNB 10 and the terminal 70.

The controller 46 comprises a handover request receiver 48, a handoverenabled/disabled state judging unit 50, a handover response transmitter52, a system information transmitter 58, and a RACH preamble receiver56. Moreover, while FIG. 7 illustrates a configuration necessary forperforming a handover, the TeNB 40 has configurations necessary forcommunication control and the like in addition to the configurationdescribed above.

The handover request receiver 48 receives a handover request transmittedfrom the SeNB 10. The handover enabled/disabled state judging unit 50judges whether a handover is enabled or disabled based on whether thereare new resources that can be allocated to the terminal 70, and thelike. The handover response transmitter 52 transmits a handover responsein response to the handover request. The system information transmitter58 transmits a system information (SU-1 signal) containing accessinformation through a common channel. When it is judged that a handovercan be performed with respect to a handover request received by thehandover request receiver 48, the system information transmitter 58reduces the transmission interval of the system information so as to beshorter than the gap period. The RACH preamble receiver 56 receives aRACH preamble transmitted from the terminal 70.

FIG. 8 is a flow chart illustrating operations during a handover by theradio communication system according to the second embodiment. Theterminal 70 transmits a measurement report to the SeNB 10 currentlyengaged in communication (S30). The SeNB 10 compares the receptionquality of a radio wave from the SeNB 10 with the reception quality of aradio wave from the TeNB 40 to judge whether or not a handover should beperformed (S32). When it is judged that a handover should not beperformed (NO in S32), the SeNB 10 awaits the reception of a nextmeasurement report.

When it is judged that a handover should be performed (YES in S32), theSeNB 10 extracts a TeNB 40 having an identifier corresponding to thecell ID notified in the measurement report from the NCL 16 (S34).Subsequently, when the TeNB is a CSG cell (YES in S36), the SeNB 10transmits a handover request to the extracted TeNB 40 of the CSG cell C2(S38). When the TeNB is not a CSG cell (NO in S36), a handover of themacro cell is performed.

The TeNB 40 having received the handover request judges whether ahandover can be performed or not (S40). When a handover can be performed(YES in S40), the TeNB 40 transmits a handover response to the SeNB 10(S42). When a handover cannot be performed (NO in S40), the radiocommunication system does not perform operations of step S42 andthereafter and terminates the flow. When a handover can be performed,the TeNB 40 sets the transmission interval of the SU-1 signal shorterthan before receiving the handover request (S44), and repeatedlytransmits the SU-1 signal (S46).

The terminal 70 judges whether the SU-1 signal has been received or not(S48). If the SU-1 cannot be received over a certain period of time (NOin S48), a judgment of handover failure is made and transmitted to theSeNB (S50). In this case, “a certain period of time” signifies a periodof time corresponding to an interval between gap periods. When the SU-1signal is transmitted during a gap period, the terminal 70 can receivethe SU-1 signal. When the SU-1 signal is judged to be received (YES inS48), the terminal 70 reads out a TAID of the TeNB 40 from the SU-1signal. The terminal 70 compares the TAID of the TeNB 40 with its ownTAID and judges whether access to the TeNB 40 is permitted or not. Theterminal 70 transmits a measurement report containing an accesspermission judgment result to the SeNB 10 (S52).

Upon receiving the measurement report from the terminal 70, the SeNB 10judges whether access to the TeNB 40 is permitted or not based on themeasurement report. When access by the terminal 70 is permitted, theSeNB 10 transmits a handover command to the terminal 70 (S54). Uponreceiving the handover command, the terminal 70 starts processing for ahandover. Specifically, the terminal 70 transmits a RACH preamble forstarting uplink synchronization to the TeNB 40 (S56), and startsprocessing to connect to the TeNB 40. Upon receiving the RACH preamble,the TeNB 40 restores the transmission interval of the SU-1 signal to theinterval prior to the start of handover processing (S58). This concludesthe description of the radio communication system according to thesecond embodiment.

The TeNB 40 according to the second embodiment adopts a configurationthat shortens the transmission interval of an SU-1 signal to betransmitted to the terminal 70 as compared to before receiving ahandover request when it is judged that a handover can be performed.Therefore, the terminal 70 is able to reliably receive the SU-1 signalcontaining access information transmitted from the TeNB 40 during afirst gap period after shortening the transmission interval.

FIGS. 9 and 10 are diagrams illustrating an example of a flow of signalstransmitted and received during a handover by the radio communicationsystem according to the second embodiment. FIG. 9 illustrates a flow ofsignals when the terminal 70 approaches a TeNB 40 to which access ispermitted. FIG. 10 illustrates a flow of signals when the terminal 70approaches a TeNB 40 to which access is not permitted.

As illustrated in FIG. 9, since the TeNB 40 according to the secondembodiment transmits the SU-1 signal at an interval that is shorter thanthe gap period after receiving the handover request and returning ahandover response, the terminal 70 can receive the SU-1 signaltransmitted from the access-permitted TeNB 40 during a first gap periodafter shortening the transmission interval of the SU-1 signal.Accordingly, a handover can be performed in a short period of time.

As illustrated in FIG. 10, in the second embodiment, since an SU-1signal is also transmitted from a TeNB 40 to which access from theterminal 70 is not permitted at an interval shorter than the gap period,the terminal 70 is able to know that access to the TeNB 40 is notpermitted upon receiving the SU-1 signal based on access informationincluded in the SU-1 signal.

As illustrated in FIG. 10, the terminal 70 does not transmit a RACHpreamble to a TeNB 40 to which access is not permitted. In addition, assimilarly illustrated in FIG. 10, the terminal 70 does not transmit aRACH preamble to a TeNB 40 to which access is permitted when theterminal 70 is remote from the TeNB 40. The TeNB 40 may use a timer as atrigger to restore the transmission interval of the SU-1 signal to itsoriginal interval. In other words, the TeNB 40 performs processing forrestoring the original transmission interval of the SU-1 signal upon thelapse of a certain period of time after the transmission interval of theSU-1 signal is shortened. In this case, “a certain period of time”signifies a period of time corresponding to an interval between gapperiods.

While an example in which the transmission interval of the SU-1 signalis shortened compared to the gap period has been described above in thepresent embodiment, the transmission interval of the SU-1 signal afterbeing once shortened may be longer than the gap period. By shorteningthe transmission interval of the SU-1 signal before receiving thehandover request, an advantageous effect can be gained in that theprobability of receiving the SU-1 signal can be increased as compared tobefore receiving the handover request. Such an aspect is also to beincluded in the present invention.

FIG. 11 is a flow chart illustrating operations during a handover by theradio communication system according to another aspect of the secondembodiment. The terminal 70 transmits a measurement report to the SeNB10 currently engaged in communication (S30). The SeNB 10 receives themeasurement report, compares the reception quality of a radio wave fromthe SeNB 10 with the reception quality of a radio wave from the TeNB 40to judge whether or not a handover should be performed (S32). When it isjudged that a handover should not be performed (NO in S32), the SeNB 10awaits the reception of a next measurement report.

When it is judged that a handover should be performed (YES in S32), theSeNB 10 extracts a TeNB 40 having an identifier corresponding to thecell ID notified in the measurement report from the NCL 16 (S34).Subsequently, the SeNB judges whether or not the TeNB is a base stationof a CSG cell (S36). When the TeNB is a CSG cell (YES in S36), the SeNB10 transmits an SU-1 transmission frequency change instruction to theextracted TeNB 40 of the CSG cell C2 (S39). When the TeNB is not a CSGcell (NO in S36), a handover of the macro cell is performed.

The TeNB 40 having received the SU-1 transmission frequency changeinstruction sets the transmission interval of the SU-1 signal shorterthan before receiving the handover request (S44), and repeatedlytransmits the SU-1 signal (S46).

The terminal 70 judges whether the SU-1 signal has been received or not(S48). When the SU-1 signal is transmitted during a gap period, theterminal 70 can receive the SU-1 signal. When the SU-1 signal is judgedto be received (YES in S48), the terminal 70 reads out a TAID of theTeNB 40 from the SU-1 signal. The terminal 70 compares the TAID of theTeNB 40 with its own TAID and judges whether access to the TeNB 40 ispermitted or not. The terminal 70 transmits a measurement reportcontaining an access permission judgment result to the SeNB 10 (S52). Ifthe SU-1 cannot be received over a certain period of time (NO in S48), ajudgment of handover failure is made and transmitted to the SeNB 10(S50). In this case, “a certain period of time” signifies a period oftime corresponding to an interval between gap periods.

Upon receiving the measurement report from the terminal 70, the SeNB 10judges whether access to the TeNB 40 is permitted or not based on themeasurement report. When access by the terminal 70 is permitted, theSeNB 10 transmits a handover request to the TeNB 40 (S38). The TeNB 40having received the handover request judges whether a handover can beperformed or not (S40), and when a handover can be performed, the TeNB40 transmits a handover response to the SeNB 10 (S42). Note that FIG. 11depicts a case where a handover can be performed. When a handover cannotbe performed (NO in S40), the radio communication system does notperform operations of step S42 and thereafter and terminates the flow.Upon receiving the handover response from the TeNB 40, the SeNB 10transmits a handover command to the terminal 70 (S54). Upon receivingthe handover command, the terminal 70 starts processing for a handover.Specifically, the terminal 70 transmits a RACH preamble for startinguplink synchronization to the TeNB 40 (S56), and starts processing toconnect to the TeNB 40. Upon receiving the RACH preamble, the TeNB 40restores the transmission interval of the SU-1 signal to the intervalprior to the start of handover processing (S58). This concludes thedescription about the operations during a handover by the radiocommunication system according to the other aspect of the secondembodiment.

According to the other aspect of the second embodiment, the TeNB 40adopts a configuration that shortens the transmission interval of anSU-1 signal to be transmitted to the terminal 70 as compared to beforereceiving a handover request when it is judged that a handover can beperformed. Therefore, the terminal 70 is able to reliably receive theSU-1 signal containing access information transmitted from the TeNB 40during a first gap period after shortening the transmission interval.

FIGS. 12 and 13 are diagrams illustrating an example of a flow ofsignals transmitted and received during a handover by a radiocommunication system according to the other aspect of the secondembodiment. FIG. 12 illustrates a flow of signals when the terminal 70approaches a TeNB 40 to which access is permitted, and FIG. 13illustrates a flow of signals when the terminal 70 approaches a TeNB 40to which access is not permitted.

As illustrated in FIG. 12, since the TeNB 40 according to the secondembodiment transmits the SU-1 signal at an interval that is shorter thanthe gap period, the terminal 70 can receive a dedicated signaltransmitted from the TeNB 40 to which access is permitted during a firstgap period after the start of transmission of the dedicated signal.Accordingly, a handover can be performed in a short period of time.

As illustrated in FIG. 13, in the second embodiment, since an SU-1signal is also transmitted from a TeNB 40 to which access from theterminal 70 is not permitted at an interval shorter than the gap period,the terminal 70 is able to know that access to the TeNB 40 is notpermitted upon receiving the SU-1 signal based on access informationincluded in the SU-1 signal.

Moreover, as illustrated in FIG. 13, the terminal 70 does not transmit aRACH preamble to a TeNB 40 to which access is not permitted. Assimilarly illustrated in FIG. 13, the terminal 70 does not transmit aRACH preamble to a TeNB 40 to which access is permitted when theterminal 70 is remote from the TeNB 40. The TeNB 40 may use a timer as atrigger to restore the transmission interval of the SU-1 signal to itsoriginal interval. In other words, the TeNB 40 performs processing forrestoring the original transmission interval of the SU-1 signal upon thelapse of a certain period of time after the transmission interval of theSU-1 signal is shortened. In this case, “a certain period of time”signifies a period of time corresponding to an interval between gapperiods.

While an example in which the transmission interval of the SU-1 signalis shortened compared to the gap period has been described above in thepresent embodiment, the transmission interval of the SU-1 signal afterbeing once shortened may be longer than the gap period. By shorteningthe transmission interval of the SU-1 signal as compared to beforereceiving the handover request, an advantageous effect can be gained inthat the probability of receiving the SU-1 signal can be increased ascompared to before receiving the handover request. Such an aspect isalso to be included in the present invention.

Third Embodiment

Next, a radio communication system and a base station according to athird embodiment of the present invention will be described. A basicconfiguration of a base station according to the third embodiment is thesame as the basic configuration of the base station according to thesecond embodiment (refer to FIGS. 6 and 7). However, an SeNB 10according to the third embodiment differs from the SeNB 10 according tothe second embodiment in that when judging that a handover should beperformed, the SeNB 10 only transmits a handover request to a TeNB 40permitting access by a terminal 70 that is a handover object. In thethird embodiment, a handover request transmitter 24 determines a TeNB 40with a TAID that is the same as the TAID of the terminal 70 havingtransmitted a measurement report based on an NCL 16, and transmits ahandover request to the determined TeNB 40.

FIG. 14 is a flow chart illustrating operations during a handover by theradio communication system according to the third embodiment. Basicoperations during a handover by the radio communication system accordingto the third embodiment are the same as the operations during a handoverby the radio communication system according to the second embodiment.The following description will focus on the differences from theoperations by the radio communication system according to the secondembodiment.

In the radio communication system according to the third embodiment,when the SeNB 10 judges that a handover should be performed (YES inS32), the SeNB 10 extracts TeNBs 40 corresponding to a cell ID notifiedin the measurement report from the NCL 16. Subsequently, the SeNB 10determines a TeNB 40 having the same TAID as the TAID of the terminal 70among the extracted TeNBs 40 (S35), and transmits a handover request tothe determined TeNB 40 (S36).

The operation by the TeNB 40 having received the handover request is thesame as the second embodiment. A TeNB 40 not having received thehandover request does not perform processing related to a handover andtransmits an SU-1 signal at a regular interval.

FIG. 15 is a diagram illustrating an example of a flow of signalstransmitted and received during a handover by the radio communicationsystem according to the third embodiment. As illustrated in FIG. 15, theSeNB 10 transmits a handover request to a TeNB 40 to which access ispermitted and does not transmit a handover request to a TeNB 40 to whichaccess is not permitted. Therefore, a situation where a TeNB 40 notpermitting access by the terminal 70 frequently transmits SU-1 signalscan be prevented and wasteful use of resources to transmit the SU-1signals can be avoided.

When the terminal 70 is approaching a CSG cell C2 to which access is notpermitted and has distanced itself from a CSG cell C1 to which access ispermitted, the terminal 70 is unable to receive an SU-1 signal. When theterminal 70 does not receive an SU-1 signal for a certain period of timeor, in other words, when a RACH preamble has not been transmitted eventhough a certain period of time has lapsed after shortening thetransmission interval of the SU-1 signal, the TeNB 40 restores thetransmission interval of the SU-1 signal to the original interval.

FIG. 16 is a flow chart illustrating operations during a handover by theradio communication system according to another aspect of the thirdembodiment. Basic operations during a handover by the radiocommunication system according to the third embodiment are the same asthe operations during a handover by the radio communication systemaccording to the second embodiment. The following description will focuson the differences from the operations by the radio communication systemaccording to the second embodiment.

With the radio communication system according to the third embodiment,when the SeNB 10 judges that a handover should be performed (YES inS32), the SeNB 10 extracts TeNBs 40 corresponding to a cell ID notifiedin the measurement report from the NCL 16. Subsequently, the SeNB 10determines a TeNB 40 having the same TAID as the TAID of the terminal 70among the extracted TeNBs 40 S35), and transmits an SU-1 transmissionfrequency change instruction to the determined TeNB 40 (S39).

The operation by the TeNB 40 having received the SU-1 transmissionfrequency change instruction is the same as the second embodiment (referto FIG. 11). A TeNB 40 not having received the SU-1 transmissionfrequency change instruction does not perform processing related to ahandover and transmits an SU-1 signal at a regular interval.

FIG. 17 is a diagram illustrating an example of a flow of signalstransmitted and received during a handover by a radio communicationsystem according to the other aspect of the third embodiment. Asillustrated in FIG. 17, the SeNB 10 transmits an SU-1 transmissionfrequency change instruction to a TeNB 40 to which access is permittedand does not transmit an SU-1 transmission frequency change instructionto a TeNB 40 to which access is not permitted. Therefore, a situationwhere a TeNB 40 not permitting access by the terminal 70 frequentlytransmits SU-1 signals can be prevented and wasteful use of resources totransmit the SU-1 signals can be avoided.

When the terminal 70 is approaching a CSG cell C2 to which access is notpermitted and has distanced itself from a CSG cell C1 to which access ispermitted, the terminal 70 is unable to receive an SU-1 signal. When theterminal 70 does not receive an SU-1 signal for a certain period of timeor, in other words, when a RACH preamble has not been transmitted eventhough a certain period of time has lapsed after shortening thetransmission interval of the SU-1 signal, the TeNB 40 restores thetransmission interval of the SU-1 signal to the original interval.

Fourth Embodiment

Next, a radio communication system and a base station according to afourth embodiment of the present invention will be described. A basicconfiguration of a base station according to the fourth embodiment isthe same as the basic configuration of the base station according to thethird embodiment (refer to FIGS. 6 and 7). However, the fourthembodiment differs from the third embodiment in that after receiving ahandover response, an SeNB 10 immediately transmits a handover commandto a terminal 70. In this case, the handover command contains aninstruction to have the terminal 70 receive an SU-1.

The fourth embodiment also differs from the third embodiment in that thetransmission frequency of an SU-1 signal is not changed. Accordingly,the terminal 70 having received a handover command starts receiving anSU-1 signal from the TeNB 40 after receiving the handover command. Afterreceiving the SU-1 signal, the terminal 70 compares the TAID of the TeNB40 with its own TAID and judges whether access to the TeNB 40 ispermitted or not. When access is permitted, the terminal 70 transmits aRACH preamble to the TeNB 40, and if not, transmits a handover failureto an SeNB. Consequently, the period of time required by the handovercan be reduced significantly when the terminal 70 is approaching a CSGcell to which access is permitted.

FIG. 18 is a flow chart illustrating operations during a handover by theradio communication system according to the fourth embodiment. Theterminal 70 transmits a measurement report to the SeNB 10 currentlyengaged in communication (S30). The SeNB 10 compares the receptionquality of a radio wave from the SeNB 10 with the reception quality of aradio wave from the TeNB 40 to judge whether or not a handover should beperformed (S32). When it is judged that a handover should not beperformed (NO in S32), the SeNB 10 awaits the reception of a nextmeasurement report.

When it is judged that a handover should be performed (YES in S32), theSeNB 10 extracts a TeNB 40 having an identifier corresponding to thecell ID notified in the measurement report from the NCL 16 (S34).Subsequently, the SeNB 10 judges whether or not the TeNB is a basestation of a CSG cell (S36). When the TeNB is a CSG cell (YES in S36),the SeNB 10 transmits a handover request to the extracted TeNB 40 of theCSG cell C2 (S38). When the TeNB is not a CSG cell (NO in S36), ahandover of the macro cell is performed.

The TeNB 40 having received the handover request judges whether ahandover can be performed or not (S40), and when a handover can beperformed, the TeNB 40 transmits a handover response to the SeNB 10(S42). When a handover cannot be performed (NO in S38), the radiocommunication system does not perform operations of step S40 andthereafter and terminates the flow.

Upon receiving the handover response, the SeNB 10 transmits a handovercommand to the terminal 70 (S54). The handover command contains aninstruction to the terminal to receive an SU-1 signal. Having receivedthe handover command, the terminal 70 starts reception processing forthe SU-1 signal and receives the SU-1 signal. Since the terminal 70 canreceive the SU-1 signal at a transmission frequency band of the TeNB 40after receiving the handover command, a gap period need not be set toreceive a signal from the TeNB 40. Therefore, the terminal 70 is capableof receiving the SU-1 signal from the TeNB 40 by normal receptionprocessing that does not involve providing a gap period. The terminal 70reads out a TAID of the TeNB 40 from the SU-1 signal. The terminal 70compares the TAID of the TeNB 40 with its own TAID and judges whetheraccess to the TeNB 40 is permitted or not (S62). If access to the TeNB40 has been permitted (YES in S62), a RACH preamble for starting uplinksynchronization is transmitted to the TeNB 40 (S66). On the other hand,if access to the TeNB 40 is not permitted (NO in S64), a judgment ofhandover failure is made and transmitted to the SeNB 10 (S47). Thisconcludes the description of the radio communication system according tothe fourth embodiment.

In the fourth embodiment, since the terminal 70 switches receptionfrequency bands by having the SeNB 10 instruct the terminal 70 with ahandover command to receive an SU-1 signal, the SU-1 signal can bereceived without using a gap period. Accordingly, the terminal 70 cannow reliably perform access confirmation without having the TeNB 40change the transmission interval of an SU-1 signal, thereby enabling areduction in handover time.

FIGS. 19 and 20 are diagrams illustrating an example of a flow ofsignals transmitted and received during a handover by the radiocommunication system according to the fourth embodiment. FIG. 19illustrates a flow of signals when the terminal 70 approaches a TeNB 40to which access is permitted, and FIG. 20 illustrates a flow of signalswhen the terminal 70 approaches a TeNB 40 to which access is notpermitted.

As illustrated in FIG. 19, the terminal 70 according to the fourthembodiment can receive an SU-1 signal without using a gap period.Accordingly, a handover can be performed in a short period of time.

Moreover, as illustrated in FIG. 20, the terminal 70 does not transmit aRACH preamble to a TeNB 40 to which access is not permitted. Inaddition, as similarly illustrated in FIG. 20, the terminal 70 also doesnot transmit a RACH preamble to a TeNB 40 to which access is permittedwhen the terminal 70 is remote from the TeNB 40.

While a detailed description of a base station, a radio communicationsystem, and a handover method according to the present invention hasbeen given by citing embodiments thereof, the present invention is notlimited to the embodiments described above. While examples in whichaccess information is notified to a terminal using a dedicated signal oran SU-1 signal have been described in the embodiments presented above,access information may also be notified to the terminal by othersignals. In this case, the period of time required by a handover can bereduced by shortening a transmission interval of a signal for notifyingaccess information as compared to before receiving a handover requestor, preferably, by setting the transmission interval so as to be shorterthan a gap period.

Fifth Embodiment

Next, a radio communication system and a base station according to afifth embodiment of the present invention will be described. A radiocommunication system according to the fifth embodiment reduces theperiod of time required by a handover by controlling the timing of a gapperiod of a terminal.

FIG. 23 is a diagram illustrating a configuration of a base station(SeNB) 10 that is a handover source. The SeNB 10 comprises a basestation communication interface 12 that is a communication interfacewith a TeNB 40 of a CSG cell C2, a terminal communication interface 14that is a communication interface with a terminal 70, an NCL 16 storinginformation on neighboring cells, and a controller 18 that controlscommunication with the TeNB 40 and the terminal 70. The NCL 16 containscell IDs, access information (TAD), and the like of base stationsneighboring the SeNB 10.

The controller 18 comprises a measurement report receiver 20, a handoverjudging unit 22, a handover request transmitter 24, a handover responsereceiver 26, a handover command transmitter 30, a gap controller 34, anda gap control signal transmitter 36. Moreover, while FIG. 23 illustratesa configuration necessary for performing a handover, the SeNB 10 hasconfigurations necessary for communication control and the like inaddition to the configuration described above.

The measurement report receiver 20, the handover judging unit 22, thehandover request transmitter 24, the handover response receiver 26, andthe handover command transmitter 30 have the same functions as therespective components comprising the SeNB 10 described with reference toFIG. 6. Based on a timing difference between a timing of a gap periodincluded in a measurement report from the measurement report receiver 20and a frame timing of the TeNB 40, the gap controller 34 delays thetiming of the gap period of the terminal so as to coincide with atransmission timing of an SU-1 signal of the TeNB 40. The gap controlsignal transmitter 36 notifies the gap period timing newly set by thegap controller 34 to match the timings of gap periods of the basestation 10 and the terminal 70.

FIG. 24 is a diagram illustrating a configuration of the terminal (UE)70. The terminal 70 comprises a base station communication interface 72that is a communication interface with the SeNB 10 of the macro cell C1and the TeNB 40 of the CSG cell C2, and a controller 74 that controlscommunication with the SeNB 10 and the TeNB 40.

The controller 74 comprises a synchronization signal/RS signal receiver76, a reception quality measurement unit 78 that measures receptionquality, and a measurement report transmitter 80 that transmits ameasurement report to the base station. The controller 74 also comprisesa gap control signal receiver 82 that receives a gap control signal anda gap controller 84 that controls a gap period timing based on the gapcontrol signal. The controller 74 further comprises a system informationreceiver 86 that receives a system information, an access permissionjudging unit 88 that judges access permission based on the systeminformation, a handover command receiver 90 that receives a handovercommand, and a RACH preamble transmitter 92 that transmits a RACHpreamble upon starting communication with a base station.

FIG. 25 is a flow chart illustrating operations during a handover by theradio communication system according to the fifth embodiment. Theterminal 70 performs a cell search during a gap period and detects atransmission timing from the TeNB 40. The terminal 70 calculates adifference between the transmission timing from the TeNB 40 and the gapperiod timing, and transmits a measurement report combining thedifference with a reception quality of the TeNB 40 to the SeNB 10 (S30).The SeNB 10 compares the reception quality of a radio wave from the SeNB10 with the reception quality of a radio wave from the TeNB 40 to judgewhether or not a handover should be performed (S32). When it is judgedthat a handover should not be performed (NO in S32), the SeNB 10 awaitsthe reception of a next measurement report.

When it is judged that a handover should be performed (YES in S32), theSeNB 10 extracts a TeNB 40 having an identifier corresponding to thecell ID notified in the measurement report from the NCL 16 (S35).Subsequently, when the TeNB is a CSG cell (YES in C36), the SeNB 10transmits a handover request to the extracted TeNB 40 of the CSG cell C2(S38). When the TeNB is not a CSG cell (NO in S36), a handover of themacro cell is performed.

The TeNB 40 having received the handover request judges whether ahandover can be performed or not (S40). When a handover can be performed(YES in S40), the TeNB 40 transmits a handover response to the SeNB 10(S42). When a handover cannot be performed (NO in S40), the radiocommunication system does not perform operations of step S42 andthereafter and terminates the flow.

Having received the handover response, based on a timing differencebetween the transmission timing of the TeNB 40 and the gap period timingnotified in the measurement report, the SeNB 10 determines a changedvalue of the gap period timing such that a gap period of the terminal 70matches a transmission timing of an SU-1 signal, and notifies thechanged value of the gap period timing as gap control information to theterminal 70 (S70). Subsequently, the terminal 70 and the SeNB 10simultaneously change gap period timings (S72, S74). The SeNB 10transmits a handover command to the terminal 70 (S76).

The terminal 70 detects an SU-1 signal at the changed gap period timing(S78) and confirms whether access is permitted (S80). When the terminal70 judges that access is permitted (YES in S80), the terminal 70transmits a RACH preamble for starting uplink synchronization to theTeNB 40 (S84), and starts processing to connect to the TeNB 40. When theterminal 70 judges that access is not permitted (NO in S80), theterminal 70 notifies a handover failure to the SeNB 10 (S82). Thisconcludes the description of the radio communication system according tothe fifth embodiment.

FIGS. 26 and 27 are diagrams illustrating an example of a flow ofsignals transmitted and received during a handover by the radiocommunication system according to the fifth embodiment. FIG. 26illustrates a flow of signals when the terminal 70 approaches a TeNB 40to which access is permitted, and FIG. 27 illustrates a flow of signalswhen the terminal 70 approaches a TeNB 40 to which access is notpermitted.

As illustrated in FIG. 26, according to the fifth embodiment, a handovercan be performed in a short period of time without having to shorten thetransmission interval of a system information (SU-1 signal) by the TeNB40 that is the base station of the handover destination CSG cell andwithout having to extend the gap period used by the terminal 70 toreceive the system information.

Sixth Embodiment

First, a background of a radio communication system according to a sixthembodiment will be described. In addition to access information of cellscontained in an SU-1 signal, a system information of a base stationincludes an access-prohibited cell list (hereinafter referred to as“APCL”) as a list of cells that prohibit access by a terminal. The APCLis notified to the terminal from a core network via the base station. Aterminal having received the APCL cannot be handed over to a cellincluded in the list.

At present, a system where CSG cells and macro cells use differentfrequencies (hereunder, referred to as system 1) is being considered. Inthe system 1, a terminal is able to distinguish between a CSG cell and amacro cell solely by differences in frequency. On the other hand, as afuture system (hereunder, referred to as system 2), a system isconceivable in which a CSG cell can be distinguished from a macro cellby cell IDs instead of frequencies. In the system 2, a terminal is ableto distinguish between a CSG cell and a macro cell by cell IDs. In thesystem 2, a cell ID list of neighboring CSG cells is defined as a CSGcell list and notified in the form of a system information to theterminal from a core network via the base station.

If such a system should materialize, in order to maintain compatibilityof system information between systems, a terminal used in the system 1that is an existing system must be usable in the system 2 that is afuture network.

As described above, since a terminal of the system 1 is not capable ofdistinguishing between a CSG cell and a macro cell by cell IDs, there isa possibility that the terminal may erroneously judge a CSG cell of thesystem 2 to be a macro cell. Generally, since the number of CSG cellshaving access restrictions is significantly large, attempts to access aCSG cell often result in not being able to connect to the CSG cell dueto access restrictions, causing wasting of communication resources. Thesixth embodiment provides a radio communication system designed toprevent wasting of communication resources when a terminal of the system1 is used in the system 2.

Next, a radio base station and a terminal according to the sixthembodiment will be described. FIG. 28 is a diagram illustrating aconfiguration of a base station (an SeNB and a TeNB will be collectivelyreferred to as an eNB) 100. The eNB 100 comprises a core NWcommunication interface 102 that is a communication interface with acore network, a terminal communication interface 104 that is acommunication interface with a terminal 120, and a controller 106 thatcontrols communication with the core NW and the terminal 120.

The controller 106 comprises an access-prohibited cell list receiver(hereinafter referred to as an “APCL receiver”) 108, a CSG cell listreceiver 110, a new access-prohibited cell list generator (hereinafterreferred to as a “new APCL generator”) 112, and a system informationtransmitter 114. Moreover, while FIG. 28 illustrates a configurationnecessary for system information transmission, the eNB 100 hasconfigurations necessary for communication control and the like inaddition to the configuration described above.

The APCL receiver 108 receives an APCL from the core network andtransmits the APCL to the new APCL generator 112. The CSG cell listreceiver 110 receives a CSL cell list from the core network andtransmits the CSL cell list to the new APCL generator 112.

FIG. 29A is a diagram illustrating an example of an APCL, and FIG. 29Bis a diagram illustrating a CSG cell list. An APCL is a list of cell IDsidentifying cells that do not permit access. A CSG cell list is a listindicating a range of cell IDs usable to identify a CSG cell. Asillustrated in FIG. 29B, cell IDs 300 to 350 and 450 to 500 are used asCSG cell IDs. A terminal of the system 2 can identify whether a cellidentified by a cell ID is a macro cell or a CSG cell based on whetherthe cell ID is included in these ranges.

The new APCL generator 112 loads an APCL from the APCL receiver 108 anda CSG cell list from the CSG cell list receiver 110 and generates a newAPCL. The new APCL generator 112 generates a new APCL by extracting onlyneighboring CSG cells from the CSG cell list and adding the extractedCSG list to the APCL.

FIG. 30 is a diagram illustrating an example of a new APCL generated bythe new APCL generator 112. As illustrated in FIG. 30, a new APCLcontains an APCL and a neighbor CSG cell list. In this example, whethera cell ID in a new APCL indicates an access-prohibited cell or aneighbor CSG cell is determined based on whether the cell ID is includedin a cell ID range defined in the CSG cell list.

FIG. 31 is a diagram illustrating another example of a new APCLgenerated by the new APCL generator 112. The new APCL illustrated inFIG. 31 has flags for distinguishing between CSG cells and an APCL.

When a CSG cell list from the CSG cell list receiver 110 and a new APCLfrom the new APCL generator 112 are inputted, the system informationtransmitter 114 transmits the inputted new APCL as a system informationto a terminal 120.

FIG. 32 is a diagram illustrating a configuration of the terminal (UE)120. The terminal 120 comprises a base station communication interface122 that is a communication interface with a base station and acontroller 124 that controls communication with the base station.

The controller 124 comprises a new access-prohibited cell list receiver(hereinafter referred to as a “new APCL receiver”) 126, a CSG cell listreceiver 128, and a cell list extractor 130. The new APCL receiver 126receives a new APCL from a system information transmitted from the basestation. The CSG cell list receiver 128 receives a CSG cell list fromthe system information transmitted from the base station. Based on theinputted new APCL and CSG cell list, the cell list extractor 130extracts an APCL and a neighbor CSG cell list. In this case, the APCL isextracted by excluding cells included in the CSG cell list from the newAPCL. The neighbor CSG cell list is generated from the excluded CSGcells.

Moreover, as illustrated in FIG. 31, when flags are introduced into anew APCL, an APCL and a neighbor CSG cell list can be extracted usingthe flags. Moreover, while FIG. 28 illustrates a configuration necessaryfor APCL extraction, the terminal 120 has configurations necessary forcommunication control and the like in addition to the configurationdescribed above.

FIG. 33 is a flow chart illustrating operations of APCL extraction ofthe terminal 120 in the radio communication system according to thesixth embodiment. The core network 140 transmits an APCL and a CSG celllist to the base station (eNB) 100 (S90, S92). The base station 100generates a new APCL from the APCL and the CSG cell list (S94). The basestation 100 transmits the generated new APCL as a system information tothe terminal 120 (S96). The terminal 120 extracts an APCL and a neighborCSG cell list based on the new APCL transmitted as the systeminformation (S98). Accordingly, based on the APCL and the neighbor CSGcell list, the terminal 120 can distinguish cells to which access ispermitted from cells to which access is not permitted and performappropriate radio communication processing.

In the sixth embodiment, since a new APCL that integrates an APCL and aneighbor CSG cell list is used, an entire new APCL may appear toindicate access-prohibited cells from the perspective of a terminal ofthe system 1 that is incapable of identifying CSG cells and macro cellsby cell IDs (refer to FIGS. 30 and 31). In other words, a terminal ofthe system 1 can treat a new APCL as an ordinary APCL. Accordingly,since a neighbor CSG cell of the system 2 will also be determined as anaccess-prohibited cell, the terminal of the system 1 can generally applyan access restriction to perform control so as not to access CSG cellsthat are highly likely to deny access from the terminal, therebypreventing wasting of communication resources.

As described in the above embodiment, since a terminal of the system 2can extract an APCL and a neighbor CSG cell list from a new APCL, theterminal can perform appropriate radio communication processing usingthese lists.

From the above, with the sixth embodiment, a terminal of the system 1can operate without incident in the system 2, and a terminal of thesystem 2 can receive an APCL and a neighbor CSG cell list withoutincident.

While an example in which a new APCL is transmitted to the terminal 120as a system information has been described in the present embodiment,information for transmitting a new APCL is not limited to a systeminformation and a new APCL may be transmitted in the form of otherinformation.

While there has been described what is at present considered to be thepreferred embodiments of the present invention, it will be understoodthat various modifications may be made therein, and it is intended tocover in the appended claims all such modifications as fall within thetrue spirit and scope of the present invention.

INDUSTRIAL APPLICABILITY

As described above, the present invention has an advantageous effect inthat a handover can be performed in a short period of time and is usefulfor performing a handover to a cell with access restrictions such asfrom a macro cell to a CSG cell.

The invention claimed is:
 1. An integrated circuit configured to controla process of a radio communication apparatus, wherein the processincludes: performing communication in at least one of a macrocell, whichis a first type cell, and a Closed Subscribers Group (CSG) cell, whichis a second type cell, wherein both cells are included in a radiocommunication network, and wherein the radio communication apparatus hasan inbound mobility control function to move from the first type cell tothe second type cell; determining a neighboring cell to be a measurementtarget of reception quality measurement based on a first cell list and asecond cell list, wherein the second cell list is different from thefirst cell list and includes one or more cell IDs of the second typecell; and repeatedly receiving system information from a target basestation, which is the second type cell, within a gap period used by theradio communication apparatus to suspend reception and transmission ofsignals with a source base station.
 2. The integrated circuit accordingto claim 1, wherein the process includes: determining whether the targetbase station is accessible based on the system information, andreporting a result of the accessibility determination and a measurementresult of reception quality of the neighboring cell to the target basestation.
 3. The integrated circuit according to claim 1, wherein theprocess includes: distinguishing between the first type cell and thesecond type cell based on cell IDs.
 4. A radio communication apparatuscomprising: circuitry, which, in operation, performs communication in atleast one of a macrocell, which is a first type cell, and a ClosedSubscribers Group (CSG) cell, which is a second type cell, wherein bothcells are included in a radio communication network, and wherein theradio communication apparatus has an inbound mobility control functionto move from the first type cell to the second type cell, and determinesa neighboring cell to be a measurement target of reception qualitymeasurement based on a first cell list and a second cell list, whereinthe second cell list is different from the first cell list and includesone or more cell IDs of the second type cell; and a receiver, which, inoperation, repeatedly receives system information from a target basestation, which is the second type cell, within a gap period used by theradio communication apparatus to suspend reception and transmission ofsignals with a source base station.
 5. The radio communication apparatusaccording to claim 4, wherein the circuitry, in operation, determineswhether the target base station is accessible based on the systeminformation, and reports a result of the accessibility determination anda measurement result of reception quality of the neighboring cell to thetarget base station.
 6. The radio communication apparatus according toclaim 4, wherein the circuitry, in operation, distinguishes between thefirst type cell and the second type cell based on cell IDs.
 7. A methodperformed by a radio communication apparatus, the method comprising:performing communication in at least one of a macrocell, which is afirst type cell, and a Closed Subscribers Group (CSG) cell, which is asecond type cell, wherein both cells are included in a radiocommunication network, and wherein the radio communication apparatus hasan inbound mobility control function to move from the first type cell tothe second type cell; determining a neighboring cell to be a measurementtarget of reception quality measurement based on a first cell list and asecond cell list, wherein the second cell list is different from thefirst cell list and includes one or more cell IDs of the second typecell; and repeatedly receiving system information from a target basestation, which is the second type cell, within a gap period used by theradio communication apparatus to suspend reception and transmission ofsignals with a source base station.
 8. The method according to claim 7,comprising: determining whether the target base station is accessiblebased on the system information, and reporting a result of theaccessibility determination and a measurement result of receptionquality of the neighboring cell to the target base station.
 9. Themethod according to claim 7, comprising: distinguishing between thefirst type cell and the second type cell based on cell IDs.